1. Field of the Invention
The present invention generally relates to a system for treatment of sanitary landfill leachate and, more particularly, to a biological living-filter system for reducing the toxicity of sanitary landfill leachate.
2. Setting for the Invention
When domestic, commercial, and non-hazardous industrial refuse are disposed of by sanitary landfilling, the refuse materials rapidly become exposed to anaerobic conditions. This anaerobic phenomenon often results from the actions of one, or a combination of several factors. First, the earthern cover on a sanitary landfill is poorly permeable to atmospheric oxygen. Second, refuse traditionally contains a predominant amount of biodegradable material, the principal constituent being paper. Aerobic bacterial respiration reduces available oxygen, and atmospheric transfer cannot keep pace with the demand, thereby creating an optimum environment for anaerobesis. Third, warmth, moisture, and darkness promote growth conditions favorable for anaerobes. Although many microbiological species are capable of first stage anaerobic metabolism, they have been collectively referred to as acid formers, sharing the common biochemical pathway of producing organic acids as their metabolites. Acetic acid and propionic acid represent the largest percentage of total metabolities produced. Due to the strong reducing nature of these organic byproducts, heavy metals and other compositions become cationic and readily mobile. This association of organic acids and inorganic materials has been traditionally referred to as landfill leachate. Additionally, leachate pollutants often include such materials as pathogenic bacteria, viruses, pesticides, industrial and wastewater sludges, septage, solvents, and hazardous wastes.
The extent to which leachate is able to leave a landfill location by groundwater or surface water transport has been a point of interest for many years. Studies suggest that in an arid or semiarid climate site, the water transport rates are slow, and, consequently, pollution problems are limited. Conversely, in temperate climate sites, water transport rates are fast and, consequently, leachate pollution presents a serious environmental problem. To prevent aquifer and groundwater contamination by landfill leachate, design criteria for landfills strongly encourage or require construction in soils rich in clay, located above the water table and situated at assumed safe distances from drinking and surface water resources. In spite of these precautions, leachate problems pervade many landfill locations resulting in contaminations of water resources.
More recently, attention has been focused on the concept of lining landfills with impermeable membranes, then collecting and treating leachate either off-site or on-site. Off-site treatment may involve piping the leachate to a nearby sewer system, and combining it with the municipal sanitary sewage. This off-site treatment methodology requires that the community have a municipal treatment facility capable of processing the leachate loadings; and that the concentration of leachate to wastewater be small to effectuate effective processing. For large landfill operations, on-site treatment of leachate with package plants has been attempted; but with limited success. These and other problems experienced with the prior art systems for treatment of landfill have been obviated by the present invention.
Another type of leachate treating sytem includes one or more open oxidation ponds or lagoons. This type of system tends to be relatively slow and requires a relatively large land area. In addition, the open pond is unsightly, has an objectionable odor and is a breeding ground for mosquitoes.